Continuous surface treatment method for steel wire

ABSTRACT

A method to form a phosphate coating on a steel wire, the method including: continuously forming a phosphate coating on a steel wire before being subjected to cold forming; and a descaling of jetting slurry including grit-like abrasive particles onto the steel wire before forming the phosphate coating, thereby producing a new surface on the steel wire. The method can further include a preheating of the steel wire after the descaling and before the coating treatment. The method makes it possible to form a phosphate coating on a steel wire in a short time with high productivity without causing significant forming deterioration on the surface of the steel wire.

TECHNICAL FIELD

The present invention relates to a continuous surface treatment methodfor a steel wire.

BACKGROUND ART

Phosphate coating treatment has been performed on a heat-treated steelwire such that cold forming such as wire drawing and heading is smoothlyperformed. The phosphate coating treatment is treatment for immersingthe steel wire in a coating solution tank, in which a solution ofphosphate is stored, to form a coating on a wire surface. In general, awire is treated in a batch system while the wire is kept in a coilstate. That is, a steel wire that should be subjected to the phosphatecoating treatment is immersed in a pickling tank in the first placewhile being kept coiled. Scale hindering formation of a phosphatecoating is removed (descaled) from the surface of the steel wire bypickling in the pickling tank. A coil of the descaled steel wire isimmersed in the coating solution tank. The phosphate coating treatmentis performed in the coating solution tank.

Such treatment of the batch system has an advantage that mass productionis possible and treatment cost is low. On the other hand, the treatmenthas a problem in which treatment of a large amount of waste solution isrequired and a problem in that pickling solution and coating solution donot enter a portion where a wire and a wire are in contact and treatmentunevenness of coating occurs. As a method of solving the problems, therehas been examined an inline system for continuously performingdescaling, coating, cold forming, and the like on a steel wire in astrand state.

The inline system is a system for performing, in the first place, usingshot blast or the like, physical descaling on a steel wire wound offfrom a coil and thereafter causing the steel wire to pass through acoating solution tank to form a coating. It is possible to effectivelysuppress the treatment unevenness and the like that are the problems inthe batch system. However, since a phosphate coating is formed by achemical conversion reaction, there is a problem in that a treatmenttime is long and a large facility space is necessary to increase wirespeed and improve a productive ability.

In order to solve such a problem of the inline system, techniquesdisclosed in Patent Literature 1 to Patent Literature 3 have beendeveloped.

Patent Literature 1 discloses a technique for performing blast byiron/zinc particles on a wire, forming an iron/zinc alloy layer on thesurface of the wire, and thereafter forming a phosphate coating to makeit possible to improve wire passing speed of a steel wire.

Patent Literature 2 discloses a technique for performing pretreatmentbefore phosphate coating treatment using a specific pretreatmentsolution for surface conditioning to enable crystal refining of aphosphate coating. The pretreatment solution includes phosphateparticles of Mn having a particle diameter of 5 μm or less at least atconcentration of 0.001 to 30 g/L and contains alkali metal salt orammonium salt or a mixture of the alkali metal salt and the ammoniumsalt and pH of the pretreatment solution is adjusted to 4 to 13.

Patent Literature 3 proposes a surface treatment method for a steelmaterial for ejecting onto the wire abrasive grains together with waterusing ultrahigh-pressure water jet instead of blast treatment and asurface conditioner, forming a suitable steel wire surface shape, andforming a phosphate coating in a short time.

However, the techniques described in the Patent Literature 1 to 3 haveproblems described below.

The technique described in Patent Literature 1 has a disadvantage that,since the technique includes descaling performed using special particlesof the iron/zinc particles, a significant increase in treatment cost isinvolved.

Descaling performed using the surface conditioner described in PatentLiterature 2 also has a significant effect on crystal refining of aphosphate coating. However, reaction speed itself is not high.Therefore, productivity cannot be sufficiently satisfied.

In descaling performed using the ultra-high pressure water jet of PatentLiterature 3, forming deterioration of the surface of the steel wirebecomes conspicuous as a jetting pressure of the abrasive grains and thewater is increased. As the forming deterioration is more conspicuous,when the cold forming such as the wire drawing and the heading isperformed in a later process, it is more likely that forming defectssuch as a crack of the steel wire and seizure of a die are caused.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Unexamined Patent Publication No.S62-207512

Patent Literature 2: Japanese Unexamined Patent Publication No.2003-160882

Patent Literature 3: Japanese Unexamined Patent Publication No. H7-80772

SUMMARY OF INVENTION

An object of the present invention is to provide a continuous surfacetreatment method for a steel wire that can form a phosphate coating on asteel wire in a short time at low cost and with high productivity whilesuppressing forming deterioration of the surface of the steel wire.

Provided is a method for continuously treating the surface of a steelwire before subjected the steel wire to cold forming, the methodincluding: a step of continuously forming a phosphate coating on thesteel wire; and a descaling step of jetting slurry including grit-likeabrasive particles onto the surface of the steel wire before formationof the phosphate coating, thereby producing a new surface on the surfaceof the steel wire.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing a process of a continuous surface treatmentmethod according to an embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

An embodiment of a continuous surface treatment method of the presentinvention is explained in detail below with reference to the drawings.

As shown in FIG. 1, the continuous surface treatment method of thepresent invention is performed in a manufacturing line 1 (a wire drawingline and a heading line) in which cold forming such as wire drawing isperformed on a steel wire (a steel wire rod) W. Specifically, thecontinuous surface treatment method in this embodiment includes acoating step P5 for forming a phosphate coating, which is a base of alubricant on the surface of the steel wire W in order to securelubrication between a die 5 and the steel wire W in wire drawing and alubrication treatment step P6 for applying a lubricant includingmetallic soap to the phosphate coating to coat the phosphate coatingwith the lubricant in order to increase lubricity.

More specifically, as shown in FIG. 1, the continuous surface treatmentmethod in this embodiment includes a winding-off step P1, astraightening step P2, a descaling step P3, a preheating (wirepreheating) step P4, the coating treatment P5, the lubrication treatmentstep P6, a drying step P7, a wire drawing step P8, and a coiling stepP9. In the winding-off step P1, the steel wire W is wound off from acoil of a supply stand 2. In the straightening step P2, the steel wire Wwound off in the winding-off step P1 is straightened into a linear shapeby a straightening machine 3. In the descaling step P3, scale adheringto the surface of the steel wire W is removed. In the wire preheatingstep P4, preheating of the steel wire W after the descaling isperformed. In the coating treatment P5, the steel wire W after thepreheating is immersed in a coating solution tank. A phosphate coatingis formed on the surface of the steel wire in the coating treatment P5.In the lubrication treatment step P6, a lubricant such as metallic soapis applied to the steel wire after the coating treatment to coat thesteel wire with the coating. The lubricant forms a necessary lubricationstate between the surface of the steel wire W and the die when coldforming is performed in the wire drawing step P8 in a later stage of thelubrication treatment step P6. In the coiling step P9, the steel wire Wafter being subjected to the cold forming such as the wire drawing inthis way is coiled.

The preheating step P4 between the descaling step P3 and the coatingtreatment step P5 may be omitted according to specifications. When thelubricant used in the lubrication treatment step P6 is liquid, forexample, a drying step P7 for drying the lubricant may be performedbetween the lubrication treatment step P6 and the wire drawing step P8.

The steel wire surface-treated by the continuous surface treatmentmethod and contents of the steps configuring the continuous surfacetreatment method are explained.

The steel wire W treated by the continuous surface treatment method inthis embodiment is obtained by rolling steel, stainless steel, or thelike into a long linear shape with a hot rolling mill. The steel wire Whas a diameter of 5.0 mm to 55 mm. The steel wire W is coiled after therolling. After the rolling, in order to adjust the structure, mechanicalcharacteristics, and the like of the steel wire W, heat treatment suchas annealing is sometimes applied to the steel wire W in a batch furnaceor a continuous furnace.

In the winding-off step P1, the steel wire W is wound off, in a lineshape, from the coil of the steel wire W disposed in the supply stand 2.The supply stand 2 is a facility that supports the coil of the steelwire after the hot rolling such that the axis of the coil faces theup-down direction or the horizontal direction. The winding-off of thesteel wire W is performed by, for example, unwinding the steel wire W tobe pulled out toward the upper direction of the coil or the downstreamside of the manufacturing line or winding off the steel wire W whilerotating the coil itself within a horizontal plane.

In the straightening step P3, a curl of the steel wire W is straightenedusing a straightening machine 3. The straightening machine 3 includes aplurality of straightening rolls 4. The straightening rolls 4 eliminatethe curl of the steel wire W wound off from the supply stand 2.Specifically, the steel wire W coiled shape after the hot rolling passesthrough the plurality of straightening rolls 4 in order, whereby thecurl of the steel wire W is eliminated. The steel wire straightened intothe linear shape by the straightening machine 3 is supplied to the nextdescaling step P3.

In the descaling step P3, scale is removed from the surface of the steelwire W straightened into the linear shape by the straightening machine3. In this embodiment, the removal of the scale on the surface isperformed by wet blast for jetting slurry including grit-like abrasiveparticles onto the surface of the steel wire W. Details of the descalingstep P3 are explained below.

In the preheating step P4, the steel wire W after being descaled ispreheated before the phosphate coating treatment. The preheating isperformed by, for example, spraying heated water or steam on the steelwire W from which the scale is removed or directly heating the steelwire with high-frequency induction heating or the like. Consequently,the steel material W is preheated to temperature substantially the sameas temperature for the phosphate coating treatment. The preheatingpromotes a chemical conversion reaction in forming a phosphate coatingafter the preheating and enables an increase in formation speed of thephosphate coating. Details of the preheating are also explained below.

In the coating treatment step P5, a phosphate coating is formed on thesurface of the steel wire W by immersion of the steel wire W inphosphate coating solution. The coating is formed as a base layer oflime soap, metallic soap, or the like that plays a role of a carrier fordrawing the lubricant into the die in the cold forming such as the wiredrawing and is used as the lubricant.

The phosphate coating is formed by a chemical reaction. As a treatmenttemperature is higher, the chemical reaction is promoted more.Therefore, not only the steel wire W but also the coating treatmentsolution is desirably preheated to approximately 60° C. to 80° C., whichis temperature substantially the same as the temperature of the wirepreheating. An etching reaction is promoted by increasing total acidity.Therefore, the coating reaction is considered to be also promoted.Therefore, the increasing the total acidity is effective as means forreducing a coating treatment time.

In the lubrication treatment step P6, a lubricant including metallicsoap such as lime soap is applied to the surface of the steel wire Wcoated with the phosphate coating in the coating treatment step P5 tocover the coating. When the lubricant is liquid, drying of the lubricantis desirably performed in the next drying step P7. Cold formingrepresented by the wire drawing step P8 is performed by a formingmachine (in the wire drawing step P8, a wire drawing machine 5) on thesteel wire W coated with the lubricant. The coating of the steel wire Wby the lubricant enables the cold forming while lubricating the steelwire W and makes it possible to smoothly perform forming of the steelwire.

The continuous surface treatment method is characterized in that thecontinuous surface treatment method includes the descaling step P3 aspretreatment of the coating treatment step P5 and, in the descaling stepP3, slurry including grit-like abrasive particles is jetted onto thesurface of the steel wire W. The preheating step P4 is desirablyperformed before the coating treatment step P5 as explained above. Thedescaling step P3 and the preheating step P4 make it possible to form aphosphate coating on the surface of the steel wire W in a short time andwith high productivity while suppressing forming deterioration of thesurface of the steel wire W. Details of the descaling step P3 and thepreheating step P4 are explained below.

As explained above, the descaling step P3 includes removing scale usingwet blast for jetting slurry including grit-like abrasive particles. Thewet blast is a method of jetting slurry, which is a mixture of water andhard particles, from a plurality of nozzles toward a target object withhigh-pressure air to thereby cause the slurry to collide with thesurface of the steel wire W and scrape off scale on the surface of thesteel wire W.

The plurality of nozzles are respectively disposed in a plurality ofpositions, desirably, three or more positions arranged in thecircumferential direction. Desirably, the plurality of nozzles aredisposed at substantially equal angle intervals in the circumferentialdirection around the axis of the steel wire and disposed such that thesurface of the steel wire can be covered over the entire circumferenceby a plurality of jetting regions by the plurality of nozzles. Thepositions of the nozzles are desirably distributed in a conveyingdirection of the steel wire such that the jetting regions of the nozzlesdo not interfere with one another. Specifically, the plurality ofnozzles are desirably disposed in a zigzag shape along the conveyingdirection extending along the axis of the steel wire (such that thenozzles are apportioned alternately to the left and the right along thecircumferential direction when viewed along the axis of the steel wire)or disposed in a spiral shape.

In the wet blast, it is possible to reduce an impact on a target objectby a jetted polishing material by keeping a jetting pressure of theslurry within an appropriate range. In this case, the target object isless easily damaged compared with shot blast and water jet (a jettingpressure is approximately 100 MPa). Specifically, when dry shot blastnot using liquid is performed or when the water jet is performed atextremely high air pressure even if water is used, a formingdeterioration layer produced on the surface of the steel wire tends tobe thick. It is likely that forming defects such as a crack of the steelwire and seizure of the die are caused during cold forming. On the otherhand, when the wet blast for spraying slurry, which is a mixture ofwater and hard particles, on the steel wire at an appropriate jettingpressure is performed, it is possible to reduce the thickness of theforming deterioration layer produced on the surface of the steel wirecompared with the shot blast and the water jet. It is possible to reducea working hardening amount and a working hardening depth of the steelwire surface hardened by collision of the polishing material. Therefore,in cold forming after treatment of a phosphate coating explained below,it is possible to significantly reduce the likelihood that formingdefects such as a crack of the steel wire and seizure of the die arecaused.

Specifically, the slurry is desirably jetted at a jetting pressure of,for example, 0.2 MPa or more and 0.6 MPa or less. The jetting pressureof 0.2 MPa or more enables production of a new surface explained below.The jetting pressure of 0.6 MPa or less makes the suppression of formingdefects such as a crack of the steel wire and seizure of the die moreconspicuous compared with treatment at a jetting pressure higher than0.6 MPa.

This method has a characteristic that the slurry includes grit-likeabrasive particles. The grit-like abrasive particles means a gritdefined as a metallic polishing material for blast treatment in JIS Z0311. The grit-like abrasive particles indicate particles that areformed in a square shape having line angles in a state before use and inwhich a ratio of round portions of the surfaces of the particles to theentire surface of the particles is smaller than a half. Therefore, thegrit-like abrasive particles are greatly different in shape from themetallic polishing material for shot treatment defined in JIS Z 0311,that is, “particles that do not have line angles, crushed surfaces, orother sharp surface defects in a state before use and the long diameterof which is within a double of the short diameter”.

When such grit-like abrasive particles are used, even in the wet blastfor jetting the slurry at the jetting pressure lower than the jettingpressure of the water jet as explained above, it is possible to form alarge number of concaves and convexes on the surface of the steel wire.Further, since a new surface is obtained on the surface of the steelwire by fine surface cutting by the corners of the grit-like abrasiveparticles, a chemical conversion reaction is promoted in the followingphosphate coating treatment. It is possible to obtain a phosphatecoating in a short time. In other words, a content of the grit-likeabrasive particles in the slurry only has to be set to a degree formaking it possible to produce the new surface on the surface by jettingthe slurry onto the surface of the metal wire W. The “new surface” meansa surface where the scale and an old surface layer of the metal wire Ware shaved by the jetting of the slurry and a new portion of the metalwire W on the lower side of the surface layer appears.

A type of metal configuring the grit-like abrasive particles is notlimited. From the viewpoint of forming efficiency of the descaling, themetal is desirably selected to configure particles having higherhardness than the hardness of the steel wire to be treated.Specifically, as the grit-like abrasive particles, from the viewpointof, for example, preventing post-pierce remaining particles in the steelwire surface, steel or stainless steel excellent in toughness isdesirably used.

On the other hand, in the “preheating process”, by preheating the steelwire to temperature close to the temperature of the phosphate coatingsolution used in the phosphate coating treatment, the chemicalconversion reaction in forming a phosphate coating is promoted.Therefore, a treatment condition of the preheating also greatly affectsefficiency of continuous surface treatment.

For example, when the temperature for heating the steel wire in thepreheating is less than 60° C., the effect of the preheating decreasesand the formation of the phosphate coating becomes insufficient.Conversely, the preheating at temperature exceeding 80° C. excessivelyraises the solution temperature of the phosphate coating solution tocause hydrolysis or deteriorate the coating treatment solution.Therefore, the preheating is undesirable from the viewpoint ofproductivity and cost to the contrary.

Note that, when the steel wire put in a wet state by the wet blast isdried for the preheating, it is likely that an oxide film is formed onthe surface of the steel wire during the preheating and a reaction inthe formation treatment of the phosphate coating is hindered. However,when the preheating at a low temperature of 80° C. or less is performedonly for less than 60 seconds, the oxide film is hardly formed to havelarge thickness during the preheating. Therefore, the oxide film formedduring the preheating does not cause hindrance due to the reaction inthe formation of the phosphate film after that. Therefore, it ispossible to obtain an excellent effect that the chemical conversionreaction is promoted by the preheating.

As explained above, there is provided the continuous surface treatmentmethod for the steel wire that can form the phosphate coating on thesteel wire in a short time at low cost and with high productivitywithout causing significant forming deterioration on the surface of thesteel wire. This method is a method of continuously treating the surfaceof a steel wire before being subjected to cold forming and includes astep of continuously forming a phosphate coating on the steel wire and astep of jetting slurry including grit-like abrasive particles on thesurface of the steel wire before the formation of the phosphate coating,thereby producing a new surface on the surface of the steel wire.

The use of the grit-like abrasive particles makes it possible to promotea chemical conversion reaction in the following phosphate coatingtreatment through production of a new surface on the surface of thesteel wire by fine surface cutting by corners of the grit-like abrasiveparticles and obtain a phosphate coating in a short time.

Therefore, in the continuous surface treatment method, it is alsopossible to perform the wet blast while keeping the jetting pressure ofthe slurry in an appropriate range, for example, a range of 0.2 MPa ormore and 0.6 MPa or less to promote the formation of the phosphatecoating. Consequently, it is possible to reduce a forming deteriorationlayer produced on the surface of the steel wire and a working hardeningamount, a working hardening depth, and the like of the steel wiresurface.

Further, when a preheating process for heating the steel wire performedafter the descaling process and before the coating treatment process isincluded, the temperature of the steel wire can be brought close totemperature near the temperature of the phosphate coating solution, forexample, temperature of 60° C. or more and 80° C. or less by thepreheating process. Consequently, it is possible to promote a chemicalconversion reaction in forming the phosphate coating. Therefore, it ispossible to form the phosphate coating on the steel wire in a short timeand with high productivity.

EXAMPLES

Effects of the continuous surface treatment method are explained more indetail with reference to examples and comparative examples.

Both of the examples and the comparative examples are based on anexperiment in which spheroidizing annealing, continuous surfacetreatment, wire drawing, and heading for a steel wire (ϕ11.0 mm) made ofsteel (SUJ2) are performed in this order. The continuous surfacetreatment includes descaling by wet blast, preheating, phosphate coatingtreatment, lubrication using lime soap, and drying.

Details of conditions of the experiment are as described below.

(1) Scale that should be Removed by the DescalingChemical composition: Fe₃O₄ (60%), Fe₂O₃ (40%)

Thickness: 2 μm (2) Wet Blast

Apparatus in use: General-purpose wet blast apparatus manufactured byMACOHO Co., Ltd.Polishing material: GRITTAL GH10 manufactured by VULKAN INOX GmbH.Average abrasive particle radius: 0.113 μmAir pressure: 0.4 MPaAngle of wire and nozzle: near 90°Distance between the wire and the nozzle: 100 mmAbrasive particle concentration in slurry: 15%

(3) Preheating

Heat medium in use: Hot water (40 to 80° C.)Treatment time: 60 s

(4) Phosphate Coating

Phosphate treatment agent in use: Nihon Parkerizing PB-3670XTotal acidity: 90 pt* * “pt” used for the total acidity is aconcentration unit of phosphate coating treatment solution and means amol number of NaOH of 0.1N required for neutralizing 10 ml of thephosphate coating treatment solutionCoating solution temperature: 40° C. to 80° C.Treatment time: 10 s

(5) Lubrication

Lime soap in use: Inoue Calcium Corporation MAC-A20Treatment temperature: 40° C. to 80° C.Treatment time: 10 s

(6) Others

Reduction of area of wire drawing: 12% (ϕ11 mm→ϕ10.3 mm)Heading: Forward extrusion, reduction of area 50%

A result of the experiment is shown in Table 1. In Table 1, among signsindicating a “wire drawing result” and a “heading result”, “×” indicatesthat seizure and a crack immediately occurred, “⊗” indicates thatseizure and a crack did not occur and cold forming was possible, and “Δ”indicates that seizure did not occur but the life of the die wasslightly short, and a sign of seizure was observed. The inventorsconfirmed that the steel wire had sufficient performance when there isno × in both of the “wire drawing result” and the “heading result” inthe experiment and regarded this example as a preferred example. Theinventors regarded an example, in which there is no × in only one of the“wire drawing result” and the “heading result”, as an example equivalentto the preferred example.

TABLE 1 Descaling Coating Experiment result Particle Particle Wire Totaladhesion Wire drawing Heading Method shape material speed PreheatingAcidity amount result result Example WB Sphere Steel 20 m/min No 90 pt2.7 (g/m²) X — 01 (seizure occurred) Example SB Sphere Steel 20 m/min No90 pt 2.8 (g/m²) X — 02 (seizure occurred) Example WJ Sphere Steel 20m/min No 90 pt 3.2 (g/m²) X — 03 (seizure occurred) Example WJ GritSteel 20 m/min No 90 pt 5.0 (g/m²) Δ X 04 (life of die was (crackoccurred) short) Example WB Grit Steel 20 m/min No 90 pt 5.2 (g/m²) ⊗ ⊗05 (No seizure) (No seizure) Example WB Grit Steel 40 m/min Yes 90 pt4.2 (g/m²) ⊗ Δ 06 (40° C.) (No seizure) (Surfaces gloss) Example WB GritSteel 40 m/min Yes 90 pt 5.0 (g/m²) ⊗ ⊗ 07 (60° C.) (No seizure) (Noseizure) Example WB Grit Steel 40 m/min Yes 90 pt 6.4 (g/m²) ⊗ ⊗ 08 (80°C.) (No seizure) (No seizure) Example WB Gird Alumina 40 m/min Yes 90 pt6.2 (g/m²) Δ Δ 09 (80° C.) (life of die was (life of die was short)short)

Focusing on the experiment example 1 to the experiment example 5 ofTable 1, whereas coating adhesion amounts of the experiment examples 1to 3 in which spherical abrasive particles were used for the descalingare 2.7 g/m² to 3.2 g/m², in the experiment examples 4 and 5 in whichgrit-like abrasive particles were used, coating adhesion amounts are 5.0g/m² and 5.2 g/m². It is seen that the coating adhesion amounts greatlyincreased. Therefore, it is seen that productively can be greatlyimproved by using the grid-like abrasive grains (abrasive particles) forthe descaling.

Focusing on the experiment example 4 and the experiment example 5 ofTable 1, coating adhesion amounts are substantially the same in theexperiment example 4 in which the descaling was performed using waterjet (WJ) and the experiment example 5 in which the descaling wasperformed using wet blast (WB). However, in the “wire drawing result”and the “heading result”, the wet blast (WB) indicates a wire drawingproperty and a heading property more excellent than the water jet (WJ).Specifically, in the experiment example 4, the wire drawing is possiblebut the heading is difficult. However, in the experiment examples,satisfactory results can be obtained concerning both of the wire drawingand the heading. Therefore, it is seen that the descaling by the wetblast at an appropriate jetting pressure makes the effect of suppressingforming deterioration on the surface of the steel wire and improvingformability such as the wire drawing and the heading more conspicuous.

On the other hand, focusing on the experiment example 6 to theexperiment example 8 of Table 1, it is seen that the coating adhesionamounts increased and the wire drawing property and the formability wereimproved as the preheating temperatures were higher. Whereas the coatingadhesion amount is 4.2 g/m² and gloss indicating a sign of seizure isobserved in a sample after the heading in the experiment example 6 inwhich the preheating temperature is 40° C., the coating adhesion amountsare 5.0 g/m² to 6.4 g/m² and the surface after the heading is in a moredesirable state in the experiment example 8 and the experiment example 9in which the preheating temperatures are respectively 60° C. and 80° C.Therefore, it is seen that it is possible to improve treatment wirespeed and greatly improve productivity by performing preheating prior tothe coating treatment and, desirably, performing preheating at 60° C. ormore and 80° C. or less.

In addition, as opposed to the experiment example 8 in which thematerial of the grit-like abrasive grains is steel, in the experimentexample 9 in which the material of the abrasive grains is alumina,although the coating adhesion amounts are substantially the same, thelife of the dice is slightly shorter. Therefore, the evaluations of the“wire drawing result” and the “heading result” are Δ. This is consideredto be because, since the alumna is inferior to the steel in toughness,the alumina pierced and remained in the wire during the descaling andcaused seizure during the wire drawing and the heading. Therefore, thematerial of the grit-like abrasive grains is considered to be moredesirably the steel having high toughness.

Note that the embodiment disclosed herein should be considered asillustrative in all aspects and not limiting. In particular, matters notexplicitly disclosed in the embodiment disclosed herein, for example,operation conditions and running conditions, various parameters, anddimensions, weights, volumes, and the like of components do not deviatefrom a range of normal implementation by those skilled in the art.Values that those skilled in the art can easily assume are adopted.

1: A continuous surface treatment method for a steel wire, which is forcontinuously treating a surface of a steel wire before subjecting thewire to cold forming, the method comprising: continuously forming aphosphate coating on the steel wire; and a descaling of jetting slurryincluding grit-like abrasive particles onto the surface of the steelwire before forming the phosphate coating, thereby producing a newsurface on the surface of the steel wire. 2: The continuous surfacetreatment method for a steel wire according to claim 1, furthercomprising a preheating which is performed after the descaling andbefore the coating treatment, to preheat the steel wire. 3: Thecontinuous surface treatment method for a steel wire according to claim1, wherein, in the descaling the slurry is jetted at a jetting pressureof 0.2 MPa or more and 0.6 MPa or less. 4: The continuous surfacetreatment method for a steel wire according to claim 2, wherein, in thedescaling, the slurry is jetted at a jetting pressure of 0.2 MPa or moreand 0.6 MPa or less.